2007 CERN Summer student workshop

Exercises

Discover the Higgs at the LHC:

• Find the best prediction for Higgs production at the LHC ​here.
• Find the Higgs branching ratios here​.

Choose a channel and investigate signal and background:

1. The 4 lepton final state: $pp \to H\to Z Z \to e^+e- \mu^{+ \mu}-$
   • Signal
     • Events: Parton Level​ Detector Level​
     • Plots: Parton Level​ Detector Level​
   • Background
     • Events: Parton Level​ Detector Level​
     • Plots: Parton Level​ Detector Level​
2. The 2 lepton + missing Et final state: $pp \to H\to W^{+ W}- \to e^{- \bar \nu_e \mu}+ \nu_\mu $
   • Signal
     • Events: Parton Level​ Detector Level​
     • Plots: Parton Level​ Detector Level​
   • Background
     • Events: Parton Level​ Detector Level
     • Plots: Parton Level Detector Level
3. Top associated production $pp \to t\bar tH$ with $H \to b \bar b$
   • Signal + Background samples:
     • Events: Parton Level​ Detector Level​
     • Plots: Parton Level​ Detector Level​

The Challenge

Three "black boxes" are given, in the form of event files in the LHC Olympics format and a series of selected plots:

• Box A : Events​ Plots: Parton level​ Detector level​
• Box B : Events​ Plots: Parton level​ Detector level​
• Box C : Events​ Plots: Parton lelve​ Detector level​

Black boxes contain only signal events. The students are asked to pair up the boxes above with the following models and also answer to the questions:

• Model 1 : Extra Z (zp) : What its mass? Does it have Standard Model couplings to fermions?
• Model 2 : Heavy Scalar (h): What its mass? Is it a SM Higgs?
• Model 3 : Extra W (wp+ or wp-) : What its mass? Does it have Standard Model couplings to fermions?

Useful extra information:

In the plots $H_T=\sum

p_T{vis}

+ E_T{miss}$.

• A SM-like Z' would decay (more or less democratically) into: jet jet (uu~,cc~,dd~,ss~,bb~), t tbar (tt~), lept+lept- (e+e-,mu+mu-,ta+ta-), neutrino anti-neutrino (ve ve~,vm vm~,vt vt~). It could also have couplings to SM W and Z, and in that case would decay in to ZZ and W+W-.
• An Higgs couple to particles with a strength which is proportional to the particle masses. A SM-like heavy H would decay in to t tbar (tt~), W+W-, ZZ.
• A SM-like W'+ would decay into: jet jet (ud~,cs~), t b (tb~), lept neutrino (e+ ve , mu+ vm, ta+ vt). It could also have couplings to SM W and Z, and in that case would decay in to ZW.

-- Main.FabioMaltoni - 08 Aug 2007